1. Field of the Invention
The invention relates to a vehicle drive system in which an internal combustion engine and an electric motor are provided as driving sources.
2. Description of the Related Art
In a conventional vehicle drive system (as disclosed in Japanese Patent Application Publication No. 2002-204504 (JP-A-2002-204504)), a twin-clutch type transmission using a plurality of gears is coupled to an internal combustion engine, and an electric motor is disposed between two clutch shafts of the transmission, such that a rotor shaft of the motor extends in a direction perpendicular to the clutch shafts. One of the clutch shafts is connected to the rotor shaft of the motor via a pair of bevel gears, and the other clutch shaft is connected to a case of the motor via another pair of bevel gears. In operation, a difference between the rotational speeds of the two clutch shafts is utilized to drive the motor, thereby to generate electric power. Other prior art documents relevant to the invention include, for example, Japanese Patent Application Publication No. 2004-293795 (JP-A-2004-293795).
In the drive system of JP-A-2002-204504, the internal combustion engine and the two clutch shafts are connected to each other via two or more coupling gears interposed therebetween. Therefore, the drive system inevitably suffers from losses due to engagement of the gears during transmission of power of the engine. Also, it is difficult to reduce the size of the drive system since the electric motor is disposed between the two clutch shafts. Furthermore, the rotor shaft of the motor and each of the clutch shafts, which are perpendicular to each other, are connected to each other via bevel gears, and this arrangement makes the drive system complicated in construction.